1. Field of the Invention
The present invention relates to a unique, novel, and cost effective process for preparing cyclic ketones such as indanones and chromanones, and which are useful synthetic intermediates in the agrochemical as well as the pharmaceutical industries. The synthetic utility of cyclic ketones such as indanones are also enhanced by the fact that they undergo facile Robinson annulation, producing flurenones and their analogs, which exhibit important pharmacological activities.
Although the synthesis of cyclic ketones such as 2-alkyl indanones prepared by the Mannich condensation of aryl alkyl ketones with N,N,N'N'-tetramethyldiaminomethane followed by acid-catalyzed cyclization of the resulting acrylophenones is generally suggested in the prior art, its utility is limited by the prohibitively high cost of the Mannich reagent N,N,N'N'-tetramethyldiaminomethane ([CH.sub.3).sub.2 N].sub.2 CH.sub.2) utilized in the methylenation step. An alternate methylenation technology which involves treatment of the aryl alkyl ketones with paraformaldehyde, dimethylamine hydrochloride, and acetic acid are complicated by poor yields and unwanted by-products. Direct formation of acrylophenones via Friedel Crafts acylation on the other hand fails for electron-poor aromatics and is waste producing. Thus, there is a need to be able to produce cyclic ketones such as indanones and chromanones in an efficient, cost-effective manner and in high yields.